package com.googlecode.coss.common.core.orm.mybatis.dialect;

/**
 * 
 */
public class DB2Dialect extends Dialect {

    public boolean supportsLimit() {
        return true;
    }

    public boolean supportsLimitOffset() {
        return true;
    }

    private static String getRowNumber(String sql) {
        StringBuffer rownumber = new StringBuffer(50).append("rownumber() over(");

        int orderByIndex = sql.toLowerCase().indexOf("order by");

        if (orderByIndex > 0 && !hasDistinct(sql)) {
            rownumber.append(sql.substring(orderByIndex));
        }

        rownumber.append(") as rownumber_,");

        return rownumber.toString();
    }

    private static boolean hasDistinct(String sql) {
        return sql.toLowerCase().indexOf("select distinct") >= 0;
    }

    public String getLimitString(String sql, int offset, String offsetPlaceholder, int limit,
                                 String limitPlaceholder) {
        int startOfSelect = sql.toLowerCase().indexOf("select");

        StringBuffer pagingSelect = new StringBuffer(sql.length() + 100)
                .append(sql.substring(0, startOfSelect)) // add
                                                         // the
                                                         // comment
                .append("select * from ( select ") // nest the main query in an
                                                   // outer select
                .append(getRowNumber(sql)); // add the rownnumber bit into the
                                            // outer query select list

        if (hasDistinct(sql)) {
            pagingSelect.append(" row_.* from ( ") // add another (inner) nested
                                                   // select
                    .append(sql.substring(startOfSelect)) // add the main query
                    .append(" ) as row_"); // close off the inner nested select
        } else {
            pagingSelect.append(sql.substring(startOfSelect + 6)); // add the
                                                                   // main
                                                                   // query
        }

        pagingSelect.append(" ) as temp_ where rownumber_ ");

        // add the restriction to the outer select
        if (offset > 0) {
            // int end = offset + limit;
            String endString = offsetPlaceholder + "+" + limitPlaceholder;
            pagingSelect.append("between " + offsetPlaceholder + "+1 and " + endString);
        } else {
            pagingSelect.append("<= " + limitPlaceholder);
        }

        return pagingSelect.toString();
    }
}
